Transducer having a pair of levers coupling the driving member to the translating element



July 4, 1950 a. B. BAUER 2,513,269

TRANSDUCER HAVING A PAIR OF LEVERS COUPLING THE DRIVING MEMBER TO THE TRANSLATING ELEMENT Filed May 5, 1945 3 Sheets-Sheet l 4 FIG! 2 BENJAMZNB.B('1UE'R INVENTORE 63 BY M AQME- ATTORNEY.

July 4, 1950 AUER 2,513,269

B. B. B TRANSDUCER HAVING A PAIR OF LEVERS COUPLING THE DRIVING MEMBER TO THE TRANSLATING ELEMENT Filed May 5, 1945 5 Sheets-Sheet 2 I22 I26 I43 I49 150 I2] I24 I48 I38 I50 BENJAMIN B BAUER INVENTOR.

BY QZWX m ATTORNEY.

y 1950 B. B. BAUER 2,513,269

TRANSDUCER HAVING A PAIR OF LEVERS COUPLING THE DRIVING MEMBER TO THE TRANSLATING ELEMENT Filed May 5, I945 5 Sheets-$heet 5 BEN AMI B, BAUER INVENTOR BY QZMM M ATTORNEY.

Patented July 4, 1953 TRANSDUCER HAVING A PAIR OF LEVERS COUPLING THE DRIVING MEMBER TO THE TRANSLATING ELEMENT Benjamin B. Bauer, Oak Park, 111., assignor, by

mesne assignments, to Shure Brothers, Incorporated, Chicago, 111., a corporation of Illinois Application May 5, 1945, Serial No. 592,096

7 Claims.

This invention relates to transducing devices, and particularly to devices for translating mechanical energy into electrical energy, and vice versa. It has application to transducing devices in which a torsional movement is applied to the transducing element to produce an electrical pulsation, and vice versa. It has especial application to phonograph reproducers and recorders of the crystal type.

In reproducers employing the piezoelectric crystal type of transducing element, commonly called simply a crystal, the record groove is traversed by a stylus which is supported by a driving member. The undulations of the groove are transmitted by the stylus to the driving member and a coupling member is usually provided for transmitting the vibrations of the driving member to the crystal. While the description hereinafter contained is directed primarily to the use of the device as a reproducer, it may also be used as a recorder and where reference is made in the specification and claims to the driving member and the transmission of energy therefrom to the crystal, it is understood that the direction of energy transfer may be reversed and that it may be transmitted from the crystal to the driving member and from the latter to a recording stylus.

In transducing devices, the more important desiderata are high fidelity of translation, high efficiency, minimum noise and long life. record life is also important. As will be apparent from the discussion contained hereinafter, some of these factors are interrelated.

In both reproducers and recorders piezoelectric crystals have been Widely employed because of their relatively low cost, small size and light weight. However, they possess certain inherent shortcomings, the most important of which are their great mechanical stiffness, high internal electrical impedance, and fragility.

High fidelity of translation may be obtained only if the force exerted by the stylus tip against the record surface is small. Because the contact area is small, even a small force results in high pressure. High pressure causes deformation of the side wall of a laterally cut groove, and when the pressure is excessive it produces inelastic deformation with consequent distortion, noise and record wear. It has been shown theoretically, and confirmed experimentally, that the vertical force which is required to be exerted on the stylus to keep the stylus tip simultaneously in contact with both sides of the record groove Long is substantially equal to the horizontal force 55 required to move the stylus tip laterally. This relationship holds for lateral recordings in which the groove side walls subtend an angle of approximately degrees with the vertical and in which the stylus tip radius is suiiiciently large that the tip engages the side walls, rather than the bottom, of the groove. This is the usual case. From this it follows that the stylus tip should offer minimum impedance to lateral vibration, where impedance is defined as the quotient of the force by the velocity, both measured in a lateral direction. At low and intermediate audio frequencies the impedance is predominantly that of a stiffness.

The problem of driving a torsionally stiff crystal by a driving system which must have low stiffness in order that the stylus may present minimum impedance to lateral vibration was recognized early in the art and was partially met by the introduction of a compliant driving system. This basic principle has been practically universally employed since its early adoption.

Specifically, the problem was dealt with by employing an elastic substance, such as rubber or a synthetic elastomer, as the coupling means between the driving member and the crystal. Such construction is subject to several serious disadvantages, the first of which is that the introduction of the compliance between the driving member and the crystal renders the relative angular displacement of the two dependent on the frequency of vibration and on the masses, compliances and resistances of the driving member and of the crystal and its supports.

The second disadvantage is that, although the compliance which is provided serves to reduce the torsional stiffness of the driving member as measured at the stylus tip, the potential energy stored in the compliance member is unavailable to produce strain in the crystal. In the known structures, compliance may be provided in 2. flexible stylus shank, in the coupling between the driving member and the crystal, and in crystal supports at the end of the crystal remote from t the driven end. When the driving member is angularly displaced statically, the displacement is divided among these members and the crystal itself in direct proportion to the relative compliance of the respective members. Under dynamic conditions, a similar effect is present, and the division of the displacement depends upon the frequency. The effect limits the maximum frequency at which the device can be operated satisfactorily.

The third disadvantage is that the elastic cou pling material deteriorates with age, whereby its elastic properties change and while the operation may be acceptable when the device is new, it becomes progressively and inevitably less satisfactory.

It is an object of the invention to provide a coupling means which transmits-the vibrations from the driving member to the crystal in a substantially positive manner whereby the fidelity of vide a coupling means which results in the stylus point having low impedance to lateral vibration.

It is another object of the invention to provide a coupling means which does not undergo any substantial change with age or use.

It is a further object of the invention to provide a coupling means which has a minimum tendency to fracture the crystal.

It is another object of the invention to provide a coupling means in which the angular travel of the driving-member is adjustable with respect to that of the crystal.

It is a further object to provide a coupling means which is in the unstressed condition when the device is in the normal or at rest position. I

Other objects and advantages will become apparent as the following description progresses, which is to be taken in connection with the accompanying drawings, in which:

Fig. 1 is a plan view of a transducing device of the invention with the top half of the casing removed; I

Fig. 2 is a vertical sectional view of'the' device along broken line 2-2 of Fig. 1;

Fig. 3 is an enlarged isometric view of a portion of the device;

Fig. 4 is a diagrammatic representation of the relative amplitude of the motion undergone by the driving member and the crystal of the device;

Fig. 5 is a fractional plan view of a diiferent modification of the invention; 7

Fig. 6 is a plan view of afurther modification with the top half of the casing removed;

Fig. '7 is a sectional view along broken line 1-7 of Fig. 6;

Fig. 8 is an enlarged isometric view of a pottion'of the modification shown in Figs. '6' and'l;

and 7 Figs. 9 to 13 inclusive are fragmental views of further modifications of the invention.

The device illustrated in Figs. 1 to 3 is of the torsion type, in whichthe record hasalaterally cut groove and the driving member and the end of the crystal which is coupled thereto undergo angular oscillation about a common axis, while the other end of the crystal is held stationary. The invention is not limited to this particular type of transducing device, but is applicable to other forms as will be pointed out hereinafter.

The device comprises a casing Ill composed of complementary top and bottom casing memhers [I and I2, which may be composed'of sheet metal or other suitable material and are dished to provide a compartment 13 and have cooperative flanges l4 along the side edges thereof, which flanges are adapted to abut together. At the rearward end, the edges of the casing members are turned inwardly toward each other and are shaped to provide an opening which is closed by a terminal block W of electrical insulating material, such as phenol-formaldehyde resin and laminates thereof, etc. The edges of the casing fit into grooves It of the block. At the same end, the casing members are held together by means of a bolt ll which passes through opening is in member [2, and at the forward end, the members are held together by a number of bolts (not shown) which pass through openings l9.

At the forward end and also at a point spaced inwardly from said end, the casing members are pressed inwardly to form generally circular bearings 28 and 2!, which support a generally cylindrical driving member 22 which is arranged with its axis in substantial alignment with the longitudinal axis of the casing. At locations reg-, istering with bearings 25 and 2!, driving member 22 has recesses 23 and 24 extending circumferentially, and in these recesses are mounted flexible elastic bushings 25 and 2B, which may be composed of natural or synthetic rubber or other suitable flexible elastic material. Therecesses 23 and 2t form trunnions for supporting the driving member 22, and the elastic bushings are under compression between the cooperating trunnions and bearings.

A stylus 2'! is received in a suitable opening extending generally transversely and diagonally through an intermediate portion of the drivingv member 22 as shown. The stylus is of the reproducing type but may also be of the recording type, in which case it extends perpendicularly to the driving member axis, instead of diagonally. Stylus Z'l extendsdownwardly through a clearance opening 28 in the bottom casing member [2. The side edges of opening 23 may be adapted to limit the lateral excursions of the stylus beyond a predetermined point. The stylus is clamped in place by means of a clamping screw 23 which is screwed into a threaded open-.

ing extending longitudinally into the driving member from the forward end thereof until it in tersects the stylus-receiving opening. A 001- lar seer rubber or other elastic material extends around the driving member 22 andcovers the top end of the stylus-receiving opening, andacts to cushion the top end of the stylus in case the projecting end receives a sudden blow.

In the construction described, the casing II] is arranged with its longitudinal axis generally parallel to the'record groove at the point of contact with the stylus, and the stylus oscillates laterally in response to the undulations of the groove. The oscillations of the stylus are transmitted to the driving member 22 and the latter undergoes angular oscillation about its longitudinal axis. As stated heretofore, the flexible elastic bushings 25 and 26 are under compression between bearings 2% and 2! and trunnions 23 and 2t, and there is substantially no relative motion between the bushings and the said parts, but instead the bushings undergo elastic distortion.

Within the compartment l3 and spaced rearwardly of the driving member 22 is the piezoelectric crystal 3!, which may be composed of Rochelle salt or the like, and is of the so-called Bimorph type, comprising two fiat crystal'slabs and three electrodes so constructed and arranged as to produce an E. M. F. between the electrodes upon the application of a torsional moment to the crystal. The structure of such a crystal is well known and is not shown in the drawings. The crystal 3| is in the general form of a thin fiat plate of greater length than width and is positioned with its longitudinal mechanical axis of symmetry in substantial alignment with the axis of driving member 22. The rearward end of the crystal is mounted in substantially fixed position between two blocks 32, which-may be composed of a rigid or relatively firm material, such as wood, metal, phenol-formaldehyde resin, hard rubber, 01' a relatively firm rubber or synthetic elastomer, or the like. The surfaces of the crystal may not conform exactly to the surfaces of the blocks, and if rigid blocks are employed, thin pads 33 of an elastic substance, such as rubber, may be interposed between the blocks and the crystal to provide uniform pressure upon the crystal. The thickness of the pads 33 is exaggerated in Fig. 2 for clearness. They are sufficiently thin that the rear end of the crystal undergoes little or no motion. The blocks, pads and crystal are of such dimensions that they are held firmly under compression and may be joined together and to the interior surfaces of the casing ID by means of an adhesive. The terminal conductors 35 and 36 of the crystal 3| are connected to the bladed terminals 3'! and 38 or" the device, which pass through and are held in position by terminal block I5.

In accordance with the present invention, improved means are provided for coupling the forward end of the crystal 3| to the rearward end of the driving member 22. This means comprises a bracket or stirrup member 49, preferably composed of a metal strap which extends transversely of the bottom casing half i2 approximately even with the forward end of the crystal 3| and has its end portions 4! and 42 turned upwardly substantially at right angles to the body portion. Stirrup member 49 may be fastened to the casing by soldering or other suitable means. Mounted upon the upper ends of end portions 4| and 42 is a generally V-shaped yoke 44 formed out of a single strip of material having resilient flexibility, such as spring metal. Phosphor-bronze has been found to be satisfactory, but other materials may also be used, such as aluminum, iron or steel, or the like. The end portions 15 and 46 of the yoke are mounted fixedly, as by soldering, upon the upright portions 4| and 42, respectively, of the stirrup 40. From said stirrup member, said end portions M5 and ill extend rearwardly a short distance and are then turned back upon themselves to form the loops 4? and 48, and then extend forwardly and converge toward each other to form the main arms 49 and 5a which are arranged symmetrically on opposite sides of the axis of oscillation of the driving member 22 and crystal 3|. At the loops 4? and 48, the width of the strip is reduced as shown, for a purpose which will be explained hereinafter. At the base of the V, the yoke 44 is widened to form a generally circular, fiat section 5| which. rests against the rearward end of the driving member 22. The section 5| is connected in positive motion transmitting relationship to the driving member 22 by means of a screw 52 which passes through an opening in the said section 5| and is screwed into, a threaded opening or recess in the driving member. A washer 55-5 is arranged between the head of the screw 52 and the section 5| of the yoke 44.

The portions of the arms and 5D in close proximity to. thedriving member ZZarenecked 6 inwardly toward each other locally to form sections 55 and 56 which are substantially parallel to each other. An opening is provided in each of the sections 55 and 5t and a threaded bolt 5'5 passes through the openings and has a nut 53 upon it end. Bolt 51 is adapted for adjusting the distance apart of sections 55 and 55, as will be explained hereinafter.

The main arms 49 and 50 of yoke 44 have slots which are adapted to receive the forward corner portions 60 and 6| of the crystal 3|. The said corner portions pass through the said slots and are fixedly joined to the arms 49 and 5E by means of an adhesive or other suitable means, or flexibly attached as by a permanently plasticized cement, or by elastic pads as will be described hereinafter in connection with a different modification of the invention. The yoke is arranged symmetrically with respect to the axis of sym metry of the crystal.

The operation of the device is as fo lows. As described heretofore, when the device is used as a reproducer, angular oscillation is induced in the driving member 22 by reason of the stylus 21 following the groove in the record. The forward ends of the arms 49 and 50 are joined to the section 5| at points on opposite sides of the axis of oscillation and spaced substantially therefrom, whereby they move upwardly and downwardly with the oscillations of the driving member. The rearward ends of the arms are retained against substantial lateral motion by the sections 45 and 46. The narrow loop portions 41 and 48 possess sufiicient flexibility to permit ready bending in the vertical direction. The arms 49 and 50, therefore, move vertically or laterally at their forward ends and are substantially stationary at their rearward ends. Such motion will herein be called lateral motion. The lateral motion of the arms is transmitted to the corners 6D and 6| of the crysal. When one of the arms moves upwardly the other moves downwardly and as a result the crystal undergoes a twisting action which produces an E. M. F. in the known manner. The yoke, therefore, constitutes a lever system in which the main arms 49 and 5|] constitute the levers and the looped sections 41 and 48 constitute the fulcrums. The arms 49 and 50 are substantially rigid against bending vertically, but possess substantial resilient flexibility in a horizontal direction so that they bend in the presence of a moderate force and also twist a small amount in the presence of a moderate twisting force.

Considering the single lever arm 49, when the driving member 22 induces a downward movement of the forward end of said arm, the rearward end, i. e., the looped section 41, remains stationary and the intermediate portion, i. e., that joined to the corner 6!] of the crystal 3| moves downwardly. The arm 49, therefore, is a lever of the second class, i. e., in which the work (the crystal) is located between the fulcrum (section 41) and the force (the driving member). The travel of constricted section 55 determines the travel of the corner 60 of the crystal. The relative travel of these parts is represented diagram matically in Fig. 4. Solid line 62 and dotted line 63 represent the axis of arm 49 in its upper and lower positions, respectively. Circle 54 represents the path of oscillation of section 55, circle 65 represents the path of oscillation of corner 60 of crystal 3|, the line 88 passing through the centers of circles 64 and 65 represents the axis of oscillation, and the point 67 represents thev location. of thestationary end of. the arm, i. e... loop. section 41:. While. section 55 travels throughtherelatively large arc. 68 of the circle 64-, the corner 60; of crystal 33: travels through: the relati-veiy small. arc 89 of the circle 55. The angular travel. of the crystal, therefore, is considerably less than that of the driving member- By angular travel of the crystal and the. driving member is meant the angular travel of the ends which drive: or are'driven by the lever arms. The inventionis not limited to-the form of drivingjmember shown, and the driving member may possess; flexibility and undergo some twisting. The lever arm: undergoes some slight twisting due to therestriction against turning at its rearward; end, but its resilience is such that such. twisting. takes place readily. The arm 50 undergoes azsimilar action but with its direction of motion reversed with respect to that of arm 49, with the result that crystal 3! is given a twisting motion, as explained heretofore.

The angular displacement of the crystal is adjustable. The constricted sections 55 and 560i lever: arms 49 and 58 can be drawn closer togetherand allowed to move farther apart by their own resilience by turning bolt 51. For a given angular displacement of the driving member 22, when: the sections are drawn together, the displacement of said sections is lessened, and the displacement of. the corners 683 and SI of the 1 crystal is alsolessened.

In thedevice described, the motion ofthe driving member is transmitted substantially positively to. the forward end of the crystal and substantially all of the energy imparted to the stylus isavailable to produce strain in the crystal. The

fidelityof translation is, thereforevery high. An.

additional advantage is that the impedance of the stylus to lateralv vibration is small. In' the known'deyices, the impedance is small only'when the, strain on thecrystal is small; In the device of the present invention, the lever system provides a substantially positive mechanical advantags ormultiplication of torque applied to the crystal over that applied by the record groove to. the stylus, whereby a predetermined safe strain can be appliedto the crystal by means of a. smaller force. at the stylus tip, resulting in reduced stylus wear and record wear. In addition; the mechanical efficiency of the. device is high and,. as a result, the ratio of the strength of the signal. to that. of the circuit noise is high. Since'the relation'between the two displacements, i. e., of the stylus and of the crystal, are'fixed substantially positively, they can. be established to provide the greatest amplitude of output voltage-consistentwith safe crystal operation;

Ks another advantage, the lever system: does not have any substantial natural or resonant fre quency in the direction of motion of the arms within the rangeoi transmitted frequencies and its-transmission characteristics are substantiallyuniform over said range.

An additional advantage is that the crystalis: in the unstressed condition when the device is in'the'normal or at rest position, that is, when the stylus is not in engagement with the record, and no initial stress is placed upon the crystal in the normal position. A further advantage is that the properties of the transmission: system do'not' change with age.

In the structure described, the arms of the yoke 44 need not be narrowed at the loops 4'! and 48 but may be of substantially uniform width and may be made more flexible throughout whereby bending distributed along their length. As explained. heretofore, when. the device is used as. a reproducer', the levers of the system illustrated in. Figs. r to 3 are of the second class. They may-- also be of the first class, i. e., in which the fulcrum is located between the force and the work. Such a system is illustrated in Fig. 5, in which the construction and arrangement of most of the: parts are similar to those of the corresponding: parts of the construction of Figs. 1 to 3 and will not: be described in detail. The drivi'ng. member 10 is mounted for oscillation and is fixedly joined to the base of the yoke II by a screw". The yoke II' is mounted fixedly at its end portions 13 and HI- upon astirrupsupport E5. The looped portions I8- and I9 serve as fulcrums and. relative movement between the lever sections 16 and TI and the fulcrums l8 and 19 is accomplishedby' the flexing which takes place at l'oopi sections 18 andl9, which are of reduced width; similar to the sections 41 and 48 of the device-of rfigs; 1 to 3. Lever arms it and TI are extended 'rearwardly' from the loop sections it and 79 by means of extensions 82 and 83 whichare. joined, as by soldering, to said lever arms it and 1 1. Extension's82 and 83 are slotted to receive the corners of crystal B4, and thin pads 8F and 86 of an elastic material, such as firm rubber or a. synthetic elastomer, are inserted under compressionv in the slots between the edges of the arms and the top and bottom surfaces of thecrystail. The thickness of the pads 85 and EMS preferably of the order of .01 inch.

In this-construction, a lever system is provided substantially similar to that of the construction of Figs; 1 to 3, in which one lever consists of arm Ti and extension 83; and the other of arm IE3 and extension 82 The operation of the system is similar to thatof the construction of Figs. 1 to 3' with the exception that when the driving member turns in one direction the crystal is twisted in the-opposite-direction' instead of in the same direction. The'pads 85 and86- permit the turning motion which the arms undergo relativeto the crystal but transmit the lateral motion of the arms substantially positively to the crystal. This construction possesses all of the advantages described: in connection with the device of Figs. 1 to 3.

In. the modification illustrated in Figs- 6, 7 and 8-,tlie general arrangement issimilar to that ofthe modificationshown in Figs. 1 to 3. The device comprises a casing Ill formed of complementary top'andbottommembers III and H2 providingacompartment H3. The'rearward end of the casinghas an opening which is closed by a terminal. block I15; Bearings I29 and Ill are formed in the forward end of the casing, in which: are arranged? the: elastic bushings I25. and l28 whichsupport'the trunnions I23 and I24 of the driving member. I22. An. integral flat blade The. yoke I-36= serves to couple the crystal-tothe-driving member; and'consists of a, thin strip ofresilient material, such as aluminum; spring bronzegprthelike. The arms I3! and I38 thereof: are: spaced apart at their: forward ends-and.

a vibration damping member I49, composed of an elastic material, such as plasticized cellulose nitrate, may be supported between the arms by an adhesive. The arms extend rearwardly in a diverging direction on opposite sides of the axis of the driving member and at their rearward ends are joined by the transverse yoke section I39. The yoke is in the general shape of a V, with the arms spaced apart at the base of the V and connected together at the top of the V. At the rearward section I39, the yoke is retained in position by blocks I40 and MI which extend transversely of the casing and rest against the interior surfaces of the casing members II I and H2, respectively. The arrangement is such that yoke I36 is held firmly in position by the said blocks. The blocks I40 and MI are composed of a material, such as rubber or a synthetic elastomer, which is elastic and relatively firm. A firmness which produces a reading of from 55 to it when tested on the Shore durometer has been found to be satisfactory. As an alternative, one of the blocks may be composed of such a firm material and the other of a soft elastic material, such as plasticized cellulose nitrate. The forward end portions I43 and I44 of the arms of the yoke are bent into planes substantiall parallel to the axis of the driving member and spaced uniformly from opposite sides of said axis. They are provided, respectively, with forwardly opening slots I45 and I l-6. The blade I30 of the driving member I22 is received in the slots I45 and I46, and between the opposing surfaces of the blade and the edges of the slots are arranged thin pads I 41 and I48 of a. relatively firm elastic material, such as rubber or a syn thetic elastomer. Vibration damping members II and I52 of an elastic material, such as rubber or plasticized cellulose nitrate, may be inserted between the opposite sides of blade I39 and the interior surfaces of casing H9.

The rearward end portion of the crystal I56 extends through an opening in the rearward section I36 and forward corner portions of the crystal extend through openings in intermediate portions of the arms Isl and I38 of the yoke. An adhesive may be applied so as to join the parts together. The terminals I53 and I54 of the crystal are connected to terminals I55 and I56 of the device, which are mounted in the terminal block H5.

When this modification is employed as a reproducer, the stylus I2! follows the laterally cut record groove and induces angular oscillation in the driving member I22. Such angular oscillation is transmitted by the blade I3!) to the forward end portions I 43 and I44 of the yoke arms and is transformed into up and down translational motion of said arms. The arms I31 and I38 act as levers in a manner similar to that described in connection with the arms 49 and 50 of the device shown in Figs. 1 to 3. The fulcrums for the levers are the blocks I 46 and I4 I. The said blocks are sufficiently firm that there is little or no vertical movement of the section I39. At the same time, the blocks possess suflicient compliance to accommodate the slight vertical movement of the edges of the rearward portions of the said arms. If one of the blocks is of a softer elastic material, as described hereinbefore, the firm block maintains the lever system in proper alignment while the softer block absorbs some of the vibrational energy at the higher frequencies and thereby provide a smoother response.

At the forward end of the yoke I36, the motion of the driving member results in a torsional stress between the blade I36 and the yoke portions I43 and I44. The blade I36 undergoes rotary or angular motion, whereas the portions I43 and I 44 each tend to undergo a substantially linear translational motion within a single plane. The elasticity of the pads I41 and I48 is such that they comply with the stresses and provide a pivotal support for each yoke arm which accommodates any relative turning which the arm and blade tend to undergo. At the same time, the pads are suiliciently thin that there i substantially no lost motion between the driving and the driven members and the energy transmission is substantially positive. An example of a suitable thickness for the pads I41 and I48 is .01 inch, their thickness being exaggerated. in Fig. '7 for clearness.

The rearward end of the crystal I50 is restrained substantially positively by the rearward yoke section I39, while vertical motion is transmitted substantially positively to the forward corners of the crystal by the arms I3'I and I38. When one of the said forward corner portions is moved upwardly, the opposite corner portion is moved downwardly. In this modification, the lever system applies stress directly to the forward corners and the rearward end of the crystal 50 as to impart a twisting effect to the crystal and thereby generate an E. M. F. The amplitude of travel of the forward corners of the crystal is substantially less than that of the forward portions I43 and I44 of the arms. In this modification and that of Figs. 1 to 3, the levers apply stress to portions of the crystal which are symmetrical with respect to the axis thereof.

The motion of the crystal and the arms is such that the slope of their contacting surfaces, 1. e., the edge surfaces of the arms and the top and bottom surfaces of the crystal, is naturally substantially the same. This effect is promoted by the fact that the arms may turn relatively to the blade I30, as described heretofore. As a result the arms exert substantiall no bending or shearing stress upon the corner portions of the crystal. Any effect of this character which might be present is accommodated by a twisting of the resilient arms I31 and I38. Any tendency of the arms to shear the crystal may also be avoided by providing rounded edges upon the contacting surfaces of the arms. A twisting effect is imparted to the rearward section I39 of the yoke by reason of the described motion of the arms, and this effect is accommodated by the resilient flexibility of said section I39.

The modification of the yoke which is illustrated in Figs. 9 and 10 is designed to relieve the twisting effect upon the rearward section thereof. The said yoke I50 has a shape generally similar to that of yoke I36 of the device shown in Figs. 6, 7 and 8 and may be arranged in a similar organization. It comprises a rearward section I6I and two forwardly converging arms I62 and I63. The said arms, at points I54 and I65 adjacent to the rear section I6I, are twisted throughout an angle of The twisted sections of the arms introduce vertical flexibility whereby the forward portions move relatively to the rearward portions with a suiiicient degree of readiness that the twisting effect upon the rearward section I 6| is relieved substantially. With this form of yoke, the effective fulcrums are at the points IE4 and I65 and these are preferably arranged to be located approximately one third of the length of the tal.

As: explaine d heretofore; one of the purposes of the coupling mechanismii lto cause a reduction of the amplitude of the angular motion of the crystal With i'espectxto'that of the'driving mem ber. The modification shown fragmentally in Fig. 11 provides a greaterireduction factor than dothe structures described heretofore. In this modification, 2, generally'channel 'shaped clamping member ill is fitted tightly over thefiorward end of the crystal lit andhas arms H2 and H3 projecting laterally therefrom. The arms H2 and H3, passrthrough openings in the arms EM and l'iE-of the yoke. The arrangement is otherwise similar-to that'shewn in Figs. 6,"7'and 8. Moveme-nt'is'transmitted by the lever arms I'M and tl-fi tothe arms l 72 and [73 of the clamping member I'll and thence to'the'crystal Hi). The amplitude of movement imparted' to the crystal for a given amplitude of movement of the lever arms is: lessthan' in the device of Figs. 6, '7 and-'8.

The modifications described heretofore are adapted'for use with a record haVinga laterally cut-groove. The modification shownrinFigs. 1'2 and l31isiadapted for'use with a vertically out groove. The casing 280 is similar'to the casing H) of the deviceof Figs. 1 to 3, and contains a driving memberxizfll similar in construction'and arrangementto drivingmember1'22 except that the stylus-receiving opening thereof extends substantially perpendicularly to the axis insteadof diagonally. Thestylusflfli is of angular shape, havingan end portion 203 which extends into the stylus receiving opening of the driving member 20!, an intermediate portion 204 which extends generally perpendicularly to theend portion and astip portion265 which extends generally parallel to'theend portion 203. The stylus'is arranged so that intermediate portion 2% extends generally perpendicular to the axis of the driving member 20! and the tip portion Zliirests in the vertically cut groove'illfi of'the record-2M. Thetip portion 205 vibrates vertically, as the device is viewed in-Figs. 12 'and l3,"i'n response to-the undulations of the-groove-Ztii, and the end'portion 2ll3:vibrates angularly about the axis oft'hedriving member and induces angular vibration'of the driving member; The construe tion and arrangement of the crystal and the means for transmitting-motion from the driving member-to the crystal may be similar to that'of any of the transmitting means describe'dhereinbefore.

Whileth-e invention has-'beenillustrated with respect to a twister type of crystal, it is applicable also to a crystal of 'the'ben'der type. Thelever system is also adaptecl for-use with an electrostatic transducingdevice. "For example, it may be appliedtothe movable electrode '70 of the transducing' device shown in Fig. 7 of'my Patent No. 2,326,280. It is also'adapted for use with a transducing device of the electromagnetic type in which an armature is vibrated or angularly oscillated in an electromagnetic field.

While but a few embodiments of the invention are specifictlly described and illustrated, it is un'derstoodthat these are byway of example only, and that various changes may be made in structural 5 features without departing from the spirit of the: invention as the'same is defined by the appended claims.

What is claimed is:

' 1."In,a transducing device,:the'combinati'on of adriving member, means for mounting said drivinggmember for angular. oscillation about an axis thereof, a transducing element, means for.

1 2 mounting said rtransducing element at a :portion thereotapair of levers arranged respectively on opposite sides of and in spaced relation to said driving member axis-and extending in thegeneraldirection of-said "axis, means for converting oscillatory motion of said driving'member into lateral motion: of :first: portions'of; said leverszrespectively, .substantial'lyifixed fillcrums for second portions :of said levers,'said levers having openings therein at third .portionsithereof, portions. of said rtransdu'cing ielement remote from said mounted-portion thereof? extending into said openings, the arrangement'being such-that lateral motion of said third portions of said levers produces a flexing of --said transducing element.

In ::a mechanoeelectr-ic transducing device, thexcombination :of a driving member, means for mounting said drivingmember for angular oscillation about an axis, ,a transducing element, meansfor mounting said transdueing element at a portion thereof, a' pair of levers arranged respectively on oppositesides'of and in spaced relationto said axis and extendingin the: general direction of.:-said axis means for converting angular-oscillatory motion of said: driving member into lateral motion of first'portions of said levers respectively-andvice versa,-relati-vely fixed fulcrums for second portions of said levers, third portions of said. levers-being connected in motion transmitting melationship .to a pair of spaced apart portions of saidtransducing.element remote from said mountedportion. thereof.

3. The transducing device construction as claimed in claimfi in Whichthemeans for converting angular oscillatory-motion of thedriving member into lateral motion of. the levers includes an arm extending. from the driving member transversely of said aaisand beingin motiontransmitting relationship with. said levers, and-resilient compressible pads betweensaid arm and said levers.

4. In-a meohano-electric transducing device, the combinationv of a driving member,. means for mounting saioldriving member for angular oscillation about an axis, a transducingelement of the flexing type, a pair of levers arranged respectively onopposite sides of and inspaced relation tov said axis, means for converting angular oscillatory motion of saiddriving member into oppositely directedlateral motion of first portions of said levers respectively and vice versa, fulcrums for second'portions of said levers, third portions of said levers being connected in motion transmitting relationship to a pair-of spaced apart portions respectively of said transducing element, andmeansior-holding relatively fixed a portion of said transducing element spaced. from said first mentioned portions thereof.

5. In a mechano-electric transducing device, the combination of adriving member, means for mountingsaid driving member for'angular'oscih lation about'an axis, a transducing element of thefiexing type, a pair of levers arranged respectively on opposite sides of and in spaced relation to 'said axis, means for'converting angular oscillatory motion of. said drivingmember into oppositely directed lateralirnotion of first portions of said levers respectively, fulcrums for second portions. of said levers, each of said leversbeing connested in motion transmitting relationship to said transducing element along a substantial portion of the length of said lever, whereby lateral motion of said levers produces a flexing'ofsaid transducing element.

' 6. :Ina mechano-electric .transducing 1 device.

the combination of a driving member, means for mounting said driving member for angular oscillation about an axis therein, a lever, means for converting angular oscillatory motion of said driving member into lateral motion of a first por tion of said lever, a fulcrum for a second portion of said lever, a transducing element, means for connecting a third portion of said lever in motion transmitting relationship to a portion of said transducing element, and means for holding relatively fixed a portion of said transducing element spaced from said first mentioned portion thereof.

7. In a mechano-electric transducing device, the combination of a driving member, means for mounting said driving member for angular oscillation about an axis, a yoke having a midsection extending generally perpendicular to said axis and a pair of arms extending from said midseotion in the general direction of said axis, means for holding said midsection relatively fixed, means for converting angular oscillatory motion of said driving member into oppositely directed lateral motion of portions of said arms remote from said midsection and vice versa, said midseotion and said arms each having an opening therein, and a transducing element of the flexing type having spaced apart portions thereof extending respectively into said openings in said midsection and said arms, whereby lateral motion of said arms produces a flexing of said transducing element and vice versa.

BENJAMIN B. BAUER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,207,539 Gravley July 9, 1940 234:8,526 Dally May 9, 1944 2,381,861 Bauer Aug. 14, 1945 

